This invention relates to ball screw assemblies having elongated screws of the type adapted for engagement with travelling nuts which move axially between limits along the screws. The typical ball screw assembly incorporates a pair of mating helical screw and nut grooves to accommodate a plurality of rolling balls which move along a helical path via the mating grooves, the balls being axially contained within the nut. At the end of its travel cycle, each ball enters a return tube positioned to transfer the ball from one end of the nut to its starting point at the opposite end.
To the extent that ball screw systems are approximately ninety percent efficient (by comparison, acme thread-nut systems are only thirty percent efficient), ball screws are commonly utilized in environments which require great precision. For example, ball screws are typically employed in x-y table positioning, industrial motion control, and various actuator systems. Ball screws are also utilized in a variety of applications requiring conservation of energy and weight, as for example in the actuation of flaps and other control surfaces of aircraft and missiles.
A major drawback in current ball screw assembly design, however, relates to ball return tube system efficiency. Currently available ball return tube designs are compromises, to the extent that although the tubes are positioned to tangentially pick up the balls from one end of the nut and return them to the opposite end, the tubes are not positioned to collect the balls in the most efficient manner. Typically, the balls are required to make an abrupt travel path change in traversing from the groove to the return tube and vice versa. The resulting efficiency losses are translated into unnecessary noise and heat. This is a particular problem in preloaded ball screw assemblies wherein the balls are under compressive loads against the grooves in which they travel.